AIDS disease, which is primarily caused by infection of individuals with a HIV retrovirus, is now the most devastating disease in the whole world, since the number of individuals which are, to date, infected with HIV viruses is estimated to about 40 millions of individuals.
During the sole year 2001, 5 millions of individuals were infected with HIV while 3 millions of individuals have deceased in the same time. Since the discovery of the main AIDS causative agent in 1983, namely the HIV virus, extensive efforts have been made in order to understand the mechanism of action of this virus and to develop accurate methods for (i) reproducibly diagnosing the infection, as well as (ii) carrying out a prognosis of the progression of the disease in a given patient.
For surveillance purposes, the United States Centers for Disease Control (CDC) currently defines AIDS in an adult or adolescent age 13 years or older as the presence of one of 25 AIDS-indicator conditions, such as KS, PCP or disseminated MAC. In children younger than 13 years, the definition of AIDS is similar to that in adolescents and adults, except that lymphoid interstitial pneumonitis and recurrent bacterial infections are included in the list of AIDS-defining conditions (CDC, 1987b). The case definition in adults and adolescents was expanded in 1993 to include HIV infection in an individual with a CD4+ T cell count less than 200 cells per cubic millimeter (mm3) of blood (CDC, 1992). The current surveillance definition replaced criteria published in 1987 that were based on clinical conditions and evidence of HIV infection but not on CD4+ T cell determinations (CDC, 1987).
In clinical practice, symptomatology and measurements of immune function, notably levels of CD4+ T lymphocytes, are used to guide the treatment of HIV-infected persons.
HIV infects and kills CD4+ T lymphocytes in vitro, although scientists have developed immortalized T-cell lines in order to propagate HIV in the laboratory (Popovic et al., 1984; Zagury et al., 1986; Garry, 1989; Clark et al., 1991). Several mechanisms of CD4+ T cell killing have been observed in lentivirus systems in vitro and may explain the progressive loss of these cells in HIV-infected individuals (reviewed in Garry, 1989; Fauci, 1993a; Pantaleo et al., 1993a). These mechanisms include disruption of the cell membrane as HIV buds from the surface (Leonard et al., 1988) or the intracellular accumulation of heterodisperse RNAs and unintegrated DNA (Pauza et al., 1990; Koga et al., 1988). Evidence also suggests that intracellular complexing of CD4 and viral envelope products can result in cell killing (Hoxie et al., 1986).
In addition to these direct mechanisms of CD4+ T cell depletion, indirect mechanisms may result in the death of uninfected CD4+ T cells (reviewed in Fauci, 1993a; Pantaleo et al., 1993a). Uninfected cells often fuse with infected cells, resulting in giant cells called syncytia that have been associated with the cytopathic effect of HIV in vitro (Sodroski et al., 1986; Lifson et al., 1986). Uninfected cells also may be killed when free gp120, the envelope protein of HIV, binds to their surfaces, marking them for destruction by antibody-dependent cellular cytotoxicity responses (Lyerly et al., 1987). Other autoimmune phenomena may also contribute to CD4+ T cell death since HIV envelope proteins share some degree of homology with certain major histocompatibility complex type II (MHC-II) molecules (Golding et al., 1989; Koenig et al., 1988).
A number of investigators have suggested that superantigens, either encoded by HIV or derived from unrelated agents, may trigger massive stimulation and expansion of CD4+ T cells, ultimately leading to depletion or anergy of these cells (Janeway, 1991; Hugin et al., 1991). The untimely induction of a form of programmed cell death called apoptosis has been proposed as an additional mechanism for CD4+ T cell loss in HIV infection (Ameisen and Capron, 1991; Terai et al., 1991; Laurent-Crawford et al., 1991). Recent reports indicate that apoptosis occurs to a greater extent in HIV-infected individuals than in non-infected persons, both in the peripheral blood and lymph nodes (Finkel et al., 1995; Pantaleo and Fauci, 1995b; Muro-Cacho et al., 1995).
It has also been observed that HIV infects precursors of CD4+ T cells in the bone marrow and thymus and damages the microenvironment of these organs necessary for the optimal sustenance and maturation of progenitor cells (Schnittman et al., 1990b; Stanley et al., 1992). These findings may help explain the lack of regeneration of the CD4+ T cell pool in patients with AIDS (Fauci, 1993a).
Recent studies have demonstrated a substantial viral burden and active viral replication in both the peripheral blood and lymphoid tissues even early in HIV infection (Fox et al., 1989; Coombs et al., 1989; Ho et al., 1989; Michael et al., 1992; Bagnarelli et al., 1992; Pantaleo et al., 1993b; Embretson et al., 1993; Piatak et al., 1993). One group has reported that 25 percent of CD4+ T cells in the lymph nodes of HIV-infected individuals harbor HIV DNA early in the course of disease (Embretson et al., 1993). Other data suggest that HIV infection is sustained by a dynamic process involving continuous rounds of new viral infection and the destruction and replacement of over 1 billion CD4+ T cells per day (Wei et al., 1995; Ho et al., 1995).
Concerning the prognosis of progression of the disease in HIV-infected patients, a first current method consists of evaluating the increase in the number of HIV viruses which are present in a whole blood sample collected from a patient, for example by performing conventional immunoassays with antibodies specifically directed against HIV proteins, and more specifically against the HIV capsid glycoprotein gp120.
A second current method for the prognosis of progression of AIDS in a patient consists of measuring the number of copies of the HIV genome which is found in a whole blood sample collected from that patient, for example through performing a quantitative PCR amplification of the nucleic acids contained in said sample, using one or several nucleic acid primer(s) that specifically hybridise with the HIV genomic RNA.
These two methods above are useful, since numerous studies have shown that people with high levels of HIV in their blood stream are more likely to develop new AIDS-related symptom or die than individuals with lower levels of the virus.
A third current method for the prognosis of progression of AIDS in a patient consists of measuring the absolute CD4+ T-cell levels in whole blood samples from infected patients (HIV+ patients), for example by carrying out flow cytometry from a blood sample of that patient, using a labelled antibody directed against the CD4 antigen.
All of these prognosis methods above can reproducibly be used but also have their respective technical limits, in relation with, for example, their biological significance as regards the evolution of the disease.
The use of antibodies for evaluating the number of HIV viral particles present in a biological sample form a patient comprise drawbacks due to the specificity of the antibodies which are used, since it is well known that the HIV structural proteins produced by distinct HIV virus isolates significantly differ in their antigenic properties and that false negative results may thus be generated.
The measure of the number of copies of the HIV genome in a biological sample from a patient is indeed indicative that the provirus which has integrated within the infected individual's cell genome has entered into active replication cycles and that the disease is in active progression. However, this technique does not simultaneously reflect the patient's immune response against the virus progression.
The measure of the CD4+ T-cell levels in a patient is also indicative of the disease progression, since the pathogenesis of acquired immunodeficiency syndrome (AIDS) is largely attributable to the decrease in T-lymphocytes bearing the CD4 receptor (CD4+). Progressive depletion of CD4+ T-lymphocytes is associated with an increase of clinical complications. Because of this association, the measurement of CD4+ T-cell levels is used to establish decision points for monitoring the relevance of treatments against AIDS. CD4+ T-lymphocyte levels are also used as prognostic indicators in patients with human immunodeficiency virus (HIV) disease.
However, the measure of the CD4+ T-cell levels in a patient does not directly reflect the immunological status of the patient, excepted as regards the resulting immunodeficiency. Notably the measure of the CD4+ T-cell levels does not account for the status of the possible biological effectors that cause or mediate the observed CD4+ depletion, and thus of the possible biological effectors that cause this observed patient's immunodeficiency.
Indeed, it may also be mentioned that a forecast of the progression of AIDS, in a given patient infected with HIV, can also be carried out through the detection of mutations occurring in the amino acid sequence of known co-receptors for HIV that are expressed by the patient's cells, especially CD4+ cells, such as the CCR5 co-receptor, since it has been observed that HIV-infected people bearing a specific mutation in one of their two copies encoding the CCR5 co-receptor may have a slower disease course that people with two normal copies of this gene.
However, there remains a need in the art for additional methods that will allow the one skilled in the art to determine the status of progression of AIDS in patients who have been infected with a HIV virus so as to enable a more precise prognosis of the evolution of the disease, including the occurrence of, or the evolution of, the numerous well known AIDS-related diseases, and also to enable a more precise monitoring of the therapeutical treatment which may be the more beneficial to the HIV-infected patient, once taken into account the progression status of the AIDS disease. For example, there is a need in the art for novel biological markers which are indicative of the progression of AIDS, which should preferably be of biological relevance as regards the biology of the HIV infection, such as, for example, novel biological markers of relevance as regards the immunological status of the patient tested.
Indeed, these novel biological markers might be used in combination with one or several already known markers such as those cited above.
Further, there is still a need in the art for novel therapeutically useful compounds for preventing individuals from the occurrence of AIDS upon infection with a HIV virus or, more generally, for treating patients infected with a HIV virus. Particularly, in the definition of novel anti-HIV multi-therapies or HAART (“Highly Active Anti-retroviral Therapy”), there is a need to include novel pharmaceutically active compounds that will specifically be directed against other target molecules than the HIV protease and the HIV retrotranscriptase and which will act on targets involved in distinct stages of the disease. Notably, there is a need in the art for novel compounds of pharmaceutical interest that are biologically active in HIV-infected patients wherein HIV has begun to actively replicate, especially in HIV-infected patient which are close to undergo a decrease in the number of their CD4+ T-cells and who are thus susceptible to immunodeficiency, as well as in HIV-infected patients for whom the depletion of their CD4+ T-cells has already begun.